I'm trying to use equation driven splines to create a sine wave of varying lengths, calculated from the length of other features. I can create the sketch and features fine, but the equation doesn't seem to hold any references. It looks like it's resolving my referenced dimensions to a value and then treats it as a constant. Therefore when i change the referenced dimensions used to generate the original curves length, the equation driven lines are not updating because they no longer hold the references.

What am i doing wrong, the manual states you can use referenced dimensions but that's pointless if it's going to immediately solve for a constant.

Is there another way to make an equation driven line reference a variable that can be set to different values for different configurations that will update the equation appropriately?

Here's a rough idea of what i'm trying to do. I want the sine wave segment to update it's length per the referenced feature dimension equation when the overall length is updated. The sine wave curves are constrained at each end to be coincident with the fixed length ends of the feature.